Physiological parameter system

ABSTRACT

A physiological parameter system has one or more parameter inputs responsive to one or more physiological sensors. The physiological parameter system may also have quality indicators relating to confidence in the parameter inputs. A processor is adapted to combine the parameter inputs, quality indicators and predetermined limits for the parameters inputs and quality indicators so as to generate alarm outputs or control outputs or both.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/075,389 titled Physiological Parameter System, filed Mar. 8, 2005,which relates to and claims the benefit of U.S. Provisional ApplicationsNo. 60/551,165 titled Combined Physiological Parameter Monitor, filedMar. 8, 2004 and No. 60/600,640 titled Physiological ParameterController, filed Aug. 11, 2004. Each of the foregoing applications areincorporated by reference herein.

BACKGROUND OF THE INVENTION

Pulse oximetry is a widely accepted noninvasive procedure for measuringthe oxygen saturation level of arterial blood, an indicator of aperson's oxygen supply. Early detection of a low blood oxygen level iscritical in the medical field, for example in critical care and surgicalapplications, because an insufficient supply of oxygen can result inbrain damage and death in a matter of minutes. A typical pulse oximetrysystem utilizes a sensor applied to a patient's finger. The sensor hasan emitter configured with both red and infrared LEDs that project lightthrough the finger to a detector so as to determine the ratio ofoxygenated and deoxygenated hemoglobin light absorption. In particular,the detector generates first and second intensity signals responsive tothe red and IR wavelengths emitted by the LEDs after absorption byconstituents of pulsatile blood flowing within a fleshy medium, such asa finger tip. A pulse oximetry sensor is described in U.S. Pat. No.6,088,607 titled Low Noise Optical Probe, which is assigned to MasimoCorporation, Irvine, Calif. and incorporated by reference herein.

Capnography comprises the continuous analysis and recording of carbondioxide concentrations in the respiratory gases of patients. The deviceused to measure the CO₂ concentrations is referred to as a capnometer.CO₂ monitoring can be performed on both intubated and non-intubatedpatients. With non-intubated patients, a nasal cannula is used.Capnography helps to identify situations that can lead to hypoxia ifuncorrected. Moreover, it also helps in the swift differential diagnosisof hypoxia before hypoxia can lead to irreversible brain damage. Pulseoximetry is a direct monitor of the oxygenation status of a patient.Capnography, on the other hand, is an indirect monitor that helps in thedifferential diagnosis of hypoxia so as to enable remedial measures tobe taken expeditiously before hypoxia results in an irreversible braindamage.

SUMMARY OF THE INVENTION

Multiple physiological parameters, combined, provide a more powerfulpatient condition assessment tool than when any physiological parameteris used by itself. For example, a combination of parameters can providegreater confidence if an alarm condition is occurring. More importantly,such a combination can be used to give an early warning of a slowlydeteriorating patient condition as compared to any single parameterthreshold, which may not indicate such a condition for many minutes.Conditions such as hypovolemia, hypotension, and airway obstruction maydevelop slowly over time. A physiological parameter system that combinesmultiple parameters so as to provide an early warning could have a majoreffect on the morbidity and mortality outcome in such cases.

Further, a greater emphasis has been put on decreasing the pain level ofpatients on the ward. Accordingly, patients are often given an IV setupthat enables the patient to increase the level of analgesia at will. Incertain situations, however, the patient's input must be ignored so asto avoid over medication. Complications from over sedation may includehypotension, tachycardia, bradycardia, hypoventilation and apnea. Aphysiological parameter system that uses pulse oximetry monitoring ofSpO₂ and pulse rate in conjunction with patient controlled analgesia(PCA) can aid in patient safety. Utilization of conventional pulseoximetry in conjunction with PCA, however, can result in the patientbeing erroneously denied pain medication. Conventional monitors aresusceptible to patient motion, which is likely to increase with risingpain. Further, conventional monitors do not provide an indication ofoutput reliability.

Advanced pulse oximetry is motion tolerant and also provides one or moreindications of signal quality of data confidence. These indicators canbe used as arbitrators in decision algorithms for adjusting the PCAadministration and sedation monitoring. Further, advanced pulse oximetrycan provide parameters in addition to oxygen saturation and pulse rate,such as perfusion index (PI). For example hypotension can be assessed bychanges in PI, which may be associated with changes in pulse rate.Motion tolerant pulse oximetry is described in U.S. Pat. No. 6,699,194titled Signal Processing Apparatus and Method; signal quality and dataconfidence indicators are described in U.S. Pat. No. 6,684,090 titledPulse Oximetry Data Confidence Indicator, both of which are assigned toMasimo Corporation, Irvine, Calif. and incorporated by reference herein.

One aspect of a physiological parameter system in a first parameterinput responsive to a first physiological sensor and a second parameterinput responsive to a second physiological sensor. A processor isadapted to combine the parameters and predetermined limits for theparameters so as to generate an alarm output.

Another aspect of a physiological parameter system is a parameter inputresponsive to a physiological sensor and a quality indicator inputrelating to confidence in the parameter input. A processor is adapted tocombine the parameter input, the quality indicator input andpredetermined limits for the parameter input and the quality indicatorinput so as to generate a control output.

A physiological parameter method comprises the steps of inputting aparameter responsive to a physiological sensor and inputting a qualityindicator related to data confidence for the parameter. A control signalis output from the combination of the parameter and the qualityindicator. The control signal is adapted to affect the operation of amedical-related device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general block diagram of a physiological parameter systemhaving alarm, diagnostic and control outputs;

FIG. 2 is a block diagram of a physiological parameter system combiningpulse oximetry and capnography and providing alarm outputs;

FIG. 3 is a block diagram of a saturation limit alarm enhanced by ETCO₂measurements;

FIG. 4 is a block diagram of a CO₂ waveform alarm enhanced by SpO₂measurements;

FIG. 5 is a block diagram of a physiological parameter system combiningpulse oximetry and capnography and providing a diagnostic output; and

FIGS. 6-7 are block diagrams of a physiological parameter systemutilizing pulse oximetry to control patient controlled analgesia (PCA).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a physiological parameter system 100, which maycomprise an expert system, a neural-network or a logic circuit, forexample. The physiological parameter system 100 has as inputs 101 one ormore parameters from one or more physiological measurement devices, suchas a pulse oximetry 110 and/or a capnometer 120. Pulse oximeterparameters may include oxygen saturation (SpO₂), perfusion index (PI),pulse rate (PR), various signal quality and/or data confidenceindicators (Qn) and trend data, to name a few. Capnography parameterinputs may include, for example, an exhaled carbon dioxide waveform, endtidal carbon dioxide (ETCO₂) and respiration rate (RR). Signal qualityand data confidence indicators are described in U.S. Pat. No. 6,684,090cited above. The physiological parameter system 100 may also haveparameter limits 105, which may be user inputs, default conditions orotherwise predetermined thresholds within the system 100.

The inputs 101 are processed in combination to generate one or moreoutputs 102 comprising alarms, diagnostics and controls. Alarms may beused to alert medical personnel to a deteriorating condition in apatient under their care. Diagnostics may be used to assist medicalpersonnel in determining a patient condition. Controls may be used toaffect the operation of a medical-related device. Other measurementparameters 130 that can be input to the monitor may include or relate toone or more of ECG, blood glucose, blood pressure (BP), temperature (T),HbCO and MetHb, to name a few.

FIG. 2 illustrates one embodiment of a physiological parameter system200 combining pulse oximetry parameter inputs 210 and capnographyparameter inputs 220 so as to generate alarm outputs 202. Parameterlimits 205 may be user inputs, default conditions or otherwisepredetermined alarm thresholds for these parameters 210, 220. The alarms202 are grouped as pulse oximetry related 230, capnography related 240and a combination 250. For example, a pulse oximetry alarm 230 may berelated to percent oxygen saturation and trigger when oxygen saturationfalls below a predetermined percentage limit. A capnography alarm 240may be related to ETCO₂ and trigger when ETCO₂ falls below or risesabove a predetermined mm Hg pressure limit. A combination alarm 250 mayindicate a particular medical condition related to both pulse oximetryand capnography or may indicate a malfunction in either instrument.

FIG. 3 illustrates a SpO₂ alarm embodiment 300 that is responsive toETCO₂. In particular, a SpO₂ alarm 305 may be triggered sooner and mayindicate a high priority if ETCO₂ 303 is falling. That is, if ETCO₂ 303is trending down above a certain rate, the SpO₂ alarm 305 is triggeredat a higher percentage oxygen saturation threshold and alerts acaregiver to the possibility of a serious condition, e.g., a pulmonaryembolism.

As shown in FIG. 3, a slope detector 310 determines the slope 312 of theETCO₂ input 303. A slope comparator 320 compares this slope 312 to apredetermined slope limit 304. If the downward trend of ETCO₂ 303 isgreat enough, a delta value 303 is added 340 to the SpO₂ lower limit 302to generate a variable threshold 342. A threshold comparator 350compares this variable threshold 342 to the SpO₂ input 301 to generate atrigger 352 for the SpO₂ alarm 305. The alarm volume, modulation or tonemay be altered to indicate priority, based upon the slope comparatoroutput 322.

FIG. 4 illustrates a CO₂ alarm embodiment 400 that is responsive toSpO₂. In particular, morphology of the input CO₂ waveform 401 isutilized to trigger an alarm 405, and that alarm is also responsive to afalling SpO₂ 402. That is, if a pattern in the expired CO₂ waveform isdetected and SpO₂ is trending down above a certain rate, then an alarmis triggered. For example, an increasing slope of the CO₂ plateau incombination with a downward trend of SpO₂ may trigger an alarm and alerta caregiver to the possibility of an airway obstruction.

As shown in FIG. 4, a pattern extractor 410 identifies salient featuresin the CO₂ waveform and generates a corresponding feature output 412. Apattern memory 420 stores one or more sets of predetermined waveformfeatures to detect in the CO₂ input 401. The pattern memory 420 isaccessed to provide a feature template 422. A feature comparator 430compares the feature output 412 with the feature template 422 andgenerates a match output 432 indicating that a specific shape or patternhas been detected in the CO₂ waveform 401. In addition, a slope detector400 determines the slope 442 of the SpO₂ input 402. A slope comparator450 compares this slope 442 to a predetermined slope limit 404. If thedownward trend of SpO₂ 402 is great enough, a slope exceeded output 452is generated. If both the match output 432 and the slope exceeded output452 are each asserted or “true,” then a logical AND 460 generates atrigger output 462 to the alarm 470, which generates an alarm output405.

FIG. 5 illustrates a combination embodiment 500 having a diagnosticoutput 505 responsive to both SpO₂ 501 and ETCO₂ 503 inputs. A SpO₂slope detector 510 determines the slope 512 of the SpO₂ input 501 andcan be made responsive to a negative slope, a positive slope or s slopeabsolute value. A first comparator 520 compares this slope 512 to apredetermined SpO₂ slope limit 502. If the trend of SpO₂ 501 is greatenough, a SpO₂ slope exceeded output 522 is asserted. Likewise, an ETCO₂slope detector 530 determines the slope 532 of the ETCO₂ input 503. Asecond comparator 540 compares this slope 532 to a predetermined ETCO₂slope limit 504. If the downward trend of ETCO₂ 501 is great enough, anETCO₂ slope exceeded output 542 is asserted. If both slope exceededoutputs 522, 542 are asserted or “true,” a diagnostic output 505 isasserted.

In one embodiment, the slope detectors 510, 530 are responsive to anegative trend in the SpO₂ 501 and ETCO₂ 503 inputs, respectively.Accordingly, the diagnostic output 505 indicates a potential embolism orcardiac arrest. In another embodiment, the SpO₂ slope detector 510 isresponsive to negative trends in the SpO₂ 501 input, and the ETCO₂ slopedetector 530 is responsive to a positive trend in the ETCO₂ 503 input.Accordingly, the diagnostic output 505 indicates a potential airwayobstruction. The diagnostic output 505 can trigger an alarm, initiate adisplay, or signal a nursing station, to name a few.

FIGS. 6A-B illustrate a physiological parameter system 600 utilizingpulse oximetry to control patient controlled analgesia (PCA). Inparticular embodiments, a control output 608 is responsive to pulseoximetry parameters 601 only if signal quality 603 is above apredetermined threshold 604. In FIG. 6A, the control output 608 can beused to lock-out patient controlled analgesia (PCA) if pulse oximetryparameter limits have been exceeded. If signal quality is so low thatthose parameters are unreliable, however, PCA is advantageously allowed.That is, the pulse oximetry parameters are not allowed to lock-out PCAif those parameters are unreliable. By contrast, in FIG. 6B, the controloutput 608 can be used to advantageously lock-out or disable patientcontrolled analgesia (PCA) if pulse oximetry parameter limits have beenexceeded or if signal quality is so low that those parameters areunreliable.

As shown in FIG. 6A, pulse oximetry parameters 601 and correspondinglimits 602 for those parameters are one set of inputs and a signalquality measures 603 and a corresponding lower limit 604 for signalquality are another set of inputs. The parameters 601 and correspondinglimits 602 generate a combined output 703 that is asserted if any of thepulse oximetry parameter limits are exceeded. A comparator 610 comparesthe signal quality 603 input with a lower limit 604 generating a qualityoutput 612 that is asserted if the signal quality 603 drops below thatlimit 604. An AND logic 620 generates a reset 622 if the combined output702 is asserted and the quality output 612 is not asserted. The reset622 resets the timer 630 to zero. A comparator 640 compares the timeroutput 632 to a predetermined time limit 606 and generates a trigger 642if the time limit is exceeded. The trigger 642 causes the control 650 togenerate the control output 608, enabling a patient controlled analgesia(PCA), for example. In this manner, the PCA is enabled if all monitoredparameters are within set limits and signal quality is above its lowerlimit for a predetermined period of time.

As shown in FIG. 6B, the combined output 702, quality output 612, reset622, timer 630, comparator 640 and control 650 are generated asdescribed with respect to FIG. 6A, above. An OR logic 621 generates arest 622 if either the combined output 702 or the quality output 612 isasserted. In this manner, the PCA is disabled for a predetermined periodof time if any of the monitored parameters are outside of set limits orthe signal quality is below its lower limit.

FIG. 7 illustrates combined limits 700 having SpO₂ parameters 601 andcorresponding thresholds 602 as inputs and providing a combinationoutput 702. In particular, if any parameter 601 exceeds itscorresponding limit 602, the output of the corresponding comparator 710,720, 740 is asserted. An OR logic 750 is responsive to any assertedoutput 712, 722, 742 to asserted the combined output 702. For example,the combined output 702 may be asserted if SpO₂ 701 falls below a lowerlimit 709, pulse rate (PR) 703 rises above an upper limit 704 or PR 703falls below a lower limit 706.

A physiological parameter system has been disclosed in detail inconnection with various embodiments. These embodiments are disclosed byway of examples only and are not to limit the scope of the claims thatfollow. One of ordinary skill in the art will appreciate many variationsand modifications. For example, the control output 608 (FIG. 6B) can beused to control (titrate) delivered, inspired oxygen levels to patientsbased upon pulse oximetry parameters, unless signal quality is so lowthat those parameters are unreliable. One of ordinary skill in the artwill also recognize that the control output 608 (FIG. 6B) can be used tocontrol patient delivery of any of various pharmacological agents and/ormedical gases.

1. A patient monitor comprising: a first input configured to receive a trend data signal indicative of trend data related to a first parameter signal, said first parameter signal indicative of one or more physiological parameters of a patient and said first parameter signal responsive to a first physiological sensor monitoring said patient; a second input configured to receive a second parameter signal, the second parameter signal responsive to a second physiological sensor monitoring said patient; a plurality of predetermined limits for said parameter signals; and a processor adapted to combine said trend data, determined values from said second parameter signal and said limits so as to generate an alarm output.
 2. The patient monitor according to claim 1 comprising: a variable threshold responsive to said second parameter signal, said alarm output responsive to said trend data and said variable threshold.
 3. The patient monitor according to claim 2 comprising: a predetermined limit related to said second parameter signal, wherein said alarm output is triggered below said variable threshold, and wherein said variable threshold is raised in response to said second parameter signal and said predetermined limit.
 4. The patient monitor according to claim 3 wherein: said first parameter signal comprises values responsive to an SpO₂ of the patient; said second parameter signal comprises values responsive to an ETCO₂ of the patient; and said variable threshold is a lower limit for the SpO₂ that is raised in response to a downward trend in the ETCO₂ at a rate greater than said predetermined limit.
 5. The patient monitor according to claim 1 comprising: a pattern detector having a detection output responsive to said trend data, said alarm output responsive to said detection output.
 6. The patient monitor according to claim 5 further comprising: a slope detector output responsive to said second parameter signal; and a predetermined slope limit responsive to said slope detector output, wherein said alarm output is triggered only if said slope detector output exceeds said slope limit.
 7. The patient monitor according to claim 6 wherein: said first parameter signal comprises values responsive to an ETCO₂ of the patient; said second parameter signal comprises values responsive to an SpO₂ of the patient; and said alarm output is responsive to ETCO₂ morphology only when there is a sufficient downward trend in SpO₂.
 8. A physiological parameter system comprising: a trend data input relating to trend data of a parameter, the parameter responsive to a physiological sensor; a quality indicator input relating to confidence in said trend data input; a plurality of predetermined limits for said trend data input and said quality indicator input; and a processor adapted to combine said inputs and said limits so as to generate a control output.
 9. The physiological parameter system according to claim 8 wherein said control output disables patient controlled analgesia when confidence in said trend data input is low.
 10. The physiological parameter system according to claim 9 wherein said control output prevents said trend data input from disabling patient controlled analgesia when said quality indicator indicates confidence is low.
 11. A physiological parameter method comprising the steps of: inputting trend data related to a parameter, the parameter responsive to a physiological sensor; inputting a quality indicator related to data confidence for said trend data; outputting a control signal from the combination of said trend data and said quality indicator, wherein said control signal is adapted to affect the operation of a medical-related device.
 12. The physiological parameter method according to claim 11 wherein said trend data and said quality indicator are derived from a pulse oximetry sensor, said outputting step comprising the substeps of: configuring said control signal to conditionally disable said medical-related device; regulating said control signal in response to said quality indicator.
 13. The physiological parameter method according to claim 12 wherein said regulating substep comprises the substep of disabling a shut-off signal when confidence in said trend data is low.
 14. The physiological parameter method according to claim 13 wherein said regulating substep comprises the substep of enabling a shut-off signal when confidence in said trend data is high.
 15. A system for indicating a diagnostic indication of a patient condition comprising: a first sensor configured to measure a first physiological parameter and output an indication of trend data related to the first physiological parameter; a second sensor configured to measure a second physiological parameter different from said first physiological parameter and output an indication of trend data related to the second physiological parameter; and a processor which receives the outputs of the first and second sensors and determines a diagnostic indication of a patient condition from the outputs.
 16. The system of claim 15, wherein the first sensor and the second sensor comprises one or more of a pulse oximetry sensor, a blood pressure sensor, an ECG sensor, an acoustic sensor, or a capnographer. 